BI3452_24_25_PART_1

Page 24: Terminology

• Transcranial Electrical Stimulation (tES)

  • Umbrella term for methods using current passing through the scalp into brain tissue.

  • Includes:

    • Transcranial Direct Current Stimulation (tDCS)

    • Transcranial Alternating Current Stimulation (tACS)

    • Transcranial Random Noise Stimulation (tRNS)

    • Future methods not yet defined.

Page 25: tES – The Modern Era

• Reference: Nitsche and Paulus, 2000

  • Discussed excitability changes in human motor cortex due to weak tDCS.

• Measurement of tES effects:

  • Using Transcranial Magnetic Stimulation (TMS) to produce Motor Evoked Potential (MEP) in peripheral muscle.

  • Effect size is assessed by comparing pre-tES MEP and post-tES MEP amplitudes.

Page 26: tDCS over M1 and Measurement Techniques

• tDCS applied to M1 (primary motor cortex)

• TMS is used to assess MEP changes.

• EEG data collection aids in indexing cortical excitability.

Page 27: Equipment Check

• TMS Setup:

  • Wire coil stimulation setup.

  • Pulsed magnetic field with a positioning frame.

• Parameters to note:

  • Maximum field depth and stimulated brain region.

  • Recording background EMG from FDI muscle for MEP analysis.

• Latency analysis through descending volleys and MEP amplitudes measured through resting neurons (1 mV peak).

Page 28: Effects of Scalp DC Stimulation

• Conducted scalp DC stimulation for 5 minutes at 1 mA in 19 subjects:

  • Results indicated that after cathodal DC stimulation, the excitability decreased.

  • Conversely, anodal DC stimulation led to an increase in the size of the evoked response.

• Reference: Nitsche & Paulus, 2000; analysis included control conditioned responses.

Page 29: Spatial Specificity of tDCS

• Anodal/cathodal effects observed when targeting the motor cortex with contralateral forehead montage (A).

• No significant effects found with varied electrode montages (B).

• Reference: Nitsche & Paulus, 2000.

Page 30: The Neurochemistry of tDCS

• Investigating ion channel activity influenced by tDCS application in neuronal activity and response modulation.

Page 31: Linking Ion Channel Activity to tDCS

• Anodal stimulation leads to depolarization, while cathodal stimulation hyperpolarizes neurons (Purpura & McMurty, 1965).

• Investigating mechanisms and their differences between stimulation phases.

• Importance of targeting channels/receptors in short-term and long-term tDCS protocols (4s vs. 9-13min).

Page 32: tDCS On Drugs I

• Agents utilized in studies:

  • CBZ (Carbamazepine): Na+ channel blocker

  • FLU (Flunarizine): Ca2+ channel blocker

  • DMO (Dextromethorphan): NMDA channel blocker

  • PLC (Placebo)

• Reference: Nitsche et al., J Physiol, 2003.

Page 33: tDCS Over M1 and Measurement Techniques (Reiterated)

• Similar methodology as previously described for assessing MEP sizes using EEG.

Page 34: tDCS On Drugs II

• Short-term anodal tDCS effects negated by sodium channel blockers; they showed reduced effects with calcium channel blockers.

• Cathodal tDCS effects remained unchanged.

• Reference: Nitsche et al., J Physiol, 2003.

Page 35: tDCS On Drugs III

• Study with CBZ demonstrated total abolition of prolonged excitability enhancement caused by anodal tDCS under PLC condition.

• Reference: Nitsche et al., J Physiol, 2003.

Page 36: tDCS On Drugs IV

• Ca2+ channel blocker effects only impacted anodal tDCS, while cathodal responses remained intact.

• The NMDA antagonist DMO affected both anodal and cathodal tDCS after-effects.

Page 37: tDCS On Drugs - Summary

• Short-lasting tDCS (4s):

  • Linked to membrane polarization changes

  • Anodal tDCS in animals causes neuronal depolarization, with effects unclear for cathodal stimulation.

• Long-lasting tDCS (minutes):

  • Influenced by NMDA receptors, which are crucial for effects beyond rapid ionotropic changes.

  • Possible intracellular changes in Ca2+ levels implicated.

Page 38: McBreak Time!

• A humorous intermission, no academic content relevant.

Page 39: tDCS Meets MRS I

• Introduction to Magnetic Resonance Spectroscopy (MRS) for in-vivo metabolite measurement in the human brain.

• The use of MR scanners to estimate neurotransmitter concentrations.

• Reference: Stagg et al., 2009.

Page 40: tDCS Meets MRS II

• Graphical data showing changes in metabolite levels (Glx, GABA, NAA) due to anodal and cathodal tDCS compared to sham conditions.

• Study reference: Stagg CJ et al., J. Neurosci. 2009.

Page 41: tDCS Meets MRS III

• Additional graphical data indicating % changes in inhibitory (GABA) and excitatory (Glx) neurotransmitter levels post-tDCS.

Page 42: Beyond 'Direct' Current Stimulation

• Overview of additional methodologies succeeding direct stimulation in research.

Page 43: The Different “Flavours” of tES

• Visual representation highlighting variations of tES:

  • tACS: Transcranial Alternating Current Stimulation

  • tDCS: Transcranial Direct Current Stimulation

  • Sham: Control stimulation types.

Page 44: tRNS – Transcranial Random Noise Stimulation

• Defines the method: Uses random noise frequency pattern to desynchronize abnormal brain rhythms (0.1-640Hz) without true randomness.

• Literature mentions: 10 mins of stimulation yielding effects lasting 60 mins on physiological measures and behaviors (Terney et al., 2008).

Page 45: Terney et al. Study on tRNS

• Describes frequency distribution and analysis of stimulation output in research.

Page 46: tACS – Specifics

• Focuses on modulation of cortical rhythms through discrete frequency application, suitable for EEG/MEG studies.

Page 47: tACS – Entrainment Challenges

• Examines issues in MEG studies with stimulation waveforms correlated with brain rhythms, emphasizing the need to isolate intrinsic oscillations from stimulation artifacts.

Page 48: Experimental Design Overview

• Details on the electrode montage, stimulation types, and design used in the study involving 16 participants across 4 MEG visits for comprehensive data collection.

Page 49: Experimental Design - Trial Timeline

• Outlines timings in experimental trials concerning stimulus administrations and response measures.

Page 50: MEG/tDCS Integration Example

• Illustrates various conditions regarding sham and anodal tDCS pre- and post-conditions analyzed in the study.